1. Field of the Invention
This invention relates to flight simulation and more particularly to a seat vibrating system for simulating aircraft buffeting in a grounded flight trainer.
2. Description of the Prior Art
Over the years, the art of flight simulation has advanced from the early bellows-driven LINK trainers to today's highly sophisticated, computer controlled, flight and mission simulators. With ever increasing versatility and fidelity, today's simulators duplicate a broad spectrum of flight conditions, and aircraft performance in both normal and malfunction modes. Employing advanced motion systems, digital computers, visual displays and the like, present day simulators are able to generate and integrate a multiplicity of realistic flight cues to provide effective training for flight crew members.
One flight cue sometimes simulated is aircraft buffeting. At relatively high angles of attack, most aircraft will vibrate due to airflow over the wings. These vibrations are transmitted through the aircraft structure to the pilot who uses the intensity (frequency and amplitude) of the vibrations as a cue to the aircraft's attitude with respect to its maneuvering limits. Aircraft buffeting gives the pilot a warning of impending stall or loss of control.
In the past, attempts have been made to simulate aircraft buffeting by driving the motion system or base of a flight trainer to vibrate the total cockpit. This old method suffers from a number of significant disadvantages. Foremost of these is that the motion system usually does not have the frequency response capabilities to do a good job of simulating the buffeting encountered in the aircraft. Generally, only one frequency is available with a motion system; namely, one-half the update rate of the motion drive signal. However, the buffet frequency for a particular aircraft is not fixed, but, to the contrary, normally varies with angle of attack and flight conditions. Similarly, the frequency range of actual aircraft buffeting generally exceeds the maximum frequency available with a motion system drive.
A number of prior art simulators have resorted to special motion bases to vibrate a simulated aircraft fuselage. U.S. Nos. 2,787,842 and 3,376,658 illustrate this approach. Although these patented systems are capable of simulating rough air and helicopter blade stall, respectively, they apparently do so at the expense of normal flight simulation. Moreover, by vibrating the whole cockpit, these systems expose sensitive electronic and optical components, commonly mounted in and on the simulator cockpit, to vibration damage.
To overcome the latter disadvantage, one might consider mounting the pilot's seat on a moveable section of the cockpit floor; which section could be vibrated relative to the remainder of the cockpit, as was done in the early 1960's on an Edwards Air Force Base Space Flight Trainer. However, there are many aircraft cockpit arrangements where it would be extremely difficult to attach the seat to the cockpit floor. On, for example, many military aircraft with pilot ejection systems, the seat is mounted on ejection rails rather than on the floor. Further, to provide the required seat vibration with such a moveable floor section and still allow the pilot to adjust his seat in a normal manner, would require an ungainly and unduely complex system.
Similar seat adjustment problems are presented by a vibration mechanism affixed to the cockpit floor beneath the seat pan, such as that shown in British Pat. No. 1,004,005. Likewise limited space between the seat and the cockpit floor makes a scheme involving an actuator mounted to the underside of the seat pan (see British Pat. No. 979,495) impractical in many situations.
Another approach to simulating aircraft buffet is illustrated in U.S. Pat. No. 3,270,440. In the flight simulator shown therein, buffeting is simulated by creating a pulsating pressure in the air cells of the pilot's seat. Since both the frequency and amplitude of seat pulsation is fixed, this prior art system does not effectively simulate aircraft buffeting.